The invention concerns a polymer material, in particular for a medical instrument.
In a number of technical areas, but in particular in relation to medical instruments, for example balloon catheters used in interventional cardiology, components of different polymer materials are frequently used in combination with each other. The consideration of which polymer material to use arises out of the different demands which are to be made with regard to the respective components. For example, the demands made on the balloon of a medical balloon catheter are in part different from those made on the stem of the balloon catheter. Although both the balloon and stem portions of the catheter must exhibit sufficient flexibility so that they can be passed through the bloodstream to the vessel to be dilated, the balloon must expand in a defined fashion when subjected to the action of a pressure applied therein, while that is undesirable in the case of the stem.
Numerous conventional polymer materials are known which fulfil the widely varying flexibility and strength requirements for uses of this kind. For example, European patent application EP 0 697 219 A2 discloses a polymer material which is particularly suitable for a medical balloon catheter and which comprises a combination, more specifically a blend, of at least a first constituent consisting of a partly crystalline polymer, and a second constituent for enhancing the flexibility of the material. However, these conventional polymer materials suffer from the disadvantage that components produced therefrom can be connected to components of polymer materials of a different structure only to a limited extent, or with considerable complication and cost. Components of these conventional polymer materials are therefore of only limited suitability for use with components constructed using other polymer materials in a situation requiring a strong connection between the components, as is necessary, for example, in the case of the connection between the stem and the balloon in a balloon catheter. At the least, a considerable amount of complication and a considerable level of additional cost is involved in forming connections between components that are exposed to large mechanical loads. In some cases, it is even necessary to utilize expensive positively locking or adhesive connections.
Accordingly, a need still exists for a polymer material of the kind set forth above, which permits a simple connection between components produced therefrom and components produced from other polymer materials.
This invention is directed to a polymer material in the form of a polymer alloy, which is particularly suited for use in a medical instrument such as a balloon catheter. The polymer material comprises a combination of at least a first constituent, comprising a partly crystalline polymer, and a second constituent for increasing the flexibility of the material, wherein the first constituent is formed of a polyamide or a polyether block amide, and the second constituent is formed at least partly of a thermoplastic elastomer based on polystyrene (TPE-S).
In one exemplary embodiment, the polymer material of the invention comprises in a proportion in weight % of at least 30% by weight, and preferably at least 50% by weight of a copolymer of the first constituent and a thermoplastic elastomer based on polystyrene (TPE-S).
In another exemplary embodiment, the polymer material of the invention is characterized in that the proportion of the first constituent is at most 80% by weight.
In still another exemplary embodiment, the polymer material of the invention is characterized in that the proportion of the second constituent is at least 20% by weight.
In yet another exemplary embodiment, the polymer material of the invention is characterized in that the proportion of amide groups is at most substantially 15% by weight.
In still yet another exemplary embodiment, the polymer material of the invention is characterized in that the copolymer is in the form of a graft copolymer with side chains comprising polyamide or polyether amide on a principal chain comprising a thermoplastic elastomer based on polystyrene (TPE-S).
In still yet another exemplary embodiment, the polymer material of the invention is characterized in that the thermoplastic elastomer based on polystyrene (TPE-S) is formed of a styrene-butadiene-styrene copolymer (SBS), a styrene-ethene butene-styrene copolymer (SEBS), a styrene-isoprene-styrene copolymer (SIS) or a styrene-ethene propene-styrene copolymer (SEES).
In still yet another exemplary embodiment, the polymer material of the invention is characterized in that at least a part of the thermoplastic elastomerbased on polystyrene (TPE-S) of the second constituent is grafted with a compatibilizer, in particular maleic acid anhydride.
In still yet another exemplary embodiment, the polymer material of the invention is characterized in that the proportions of the constituents are matched to each other for connecting the polymer material to polyolefins, in particular polyethylene, by a connection involving joining of the materials.
In still yet another exemplary embodiment, the invention is directed to a process for forming a polymer material characterized in that at least a first constituent formed of a polyamide or a polyether block amide and a second constituent formed of a thermoplastic elastomer based on polystyrene (TPE-S) are reactively compounded to form a copolymer.
In still yet another exemplary embodiment, the invention is directed to a process for forming a polymer material characterized in that the reactive compounding operation is effected in a co-rotating twin-screw extruder, which in particular is optimized for a maximum shearing action.
In still yet another exemplary embodiment, the invention is directed to a process for forming a polymer material characterized in that the reactive compounding operation is effected in such a way that essentially all starting products are substantially completely consumed.
In still yet another exemplary embodiment, the invention is directed to a process for forming a polymer material characterized in that after the extrusion operation the polymer material is subjected to an irradiation cross-linking procedure, in particular by means of gamma radiation.
In still yet another exemplary embodiment, the invention is directed to a medical balloon catheter characterized in that its stem and/or its balloon is produced from a polymer material as set forth above.
In still yet another exemplary embodiment, the invention is directed to a medical balloon catheter characterized in that its balloon is welded to the distal catheter stem and/or the inner tube by a connection involving intimate joining of the materials concerned.